The present invention relates to a syringe pump apparatus which is adapted to deliver to and infuse into a patient a specified amount of aqueous solution per specified unit of time from a syringe within which the aqueous solution such as, for example, a medication is accommodated and, more particularly, to a syringe pump apparatus which is equipped with a drive halting mechanism adapted to halt the driving of the pumping operation when an overload has been produced in a slider section.
Conventionally, in this type of syringe pump apparatus, supply of aqueous solution is performed in the following manner. Firstly, a syringe within which an aqueous solution is accommodated is placed on a syringe holding section and, then, a flange portion of this syringe is fitted into an engaging groove formed in the syringe holding section. Then, a piston portion thereof is engaged with an engaging portion formed in a slider section Thus, the syringe is fixed to the syringe pump. Then, after having adjusted the flow rate of the aqueous solution to be infused into a patient, the syringe is pressed from above by a clamp means to thereby fixedly mount the syringe on a main body of the syringe pump apparatus. The height of the syringe is detected by a photosensor provided in the clamp means and the detection signal thus obtained is sent to the slider mechanism. Thus, the distance of the slider to be moved is determined. Thereafter, when a drive motor involved is caused to rotate, the slider mechanism is caused to operate. As a result, a specified amount of aqueous solution is infused from the syringe into the patient by way of a tube.
By the way, in the syringe pump apparatus having the described construction, it is necessary to stop the driving of the syringe pump apparatus when the aqueous solution within the syringe comes to be zero with the result that an outer casing and the slider abut against each other, or when, for example, the tube connected to the syringe has been bent or squeezed with the result that it is impossible to extrude the aqueous solution within the syringe.
A conventional halting mechanism for halting the syringe pump apparatus is arranged as follows. Namely, a drive motor is installed in the casing and has a rotational gear. This rotational gear is caused to mesh with a gear provided on a feed screw for forward movement of the slider via intermediate gears. The feed screw is thereby caused to rotate. On the other hand, the slider section has a pipe shaft on which there is provided a block section, the block section having a shaft provided thereon Said rotation of the feed screw causes the slider to be forwardly moved by the intermeshing of the feed screw with the shaft provided on the block section.
With this construction, when the slider is brought to the stoppage, it results that the rotation of the feed screw is stopped, while the drive motor is rotated. As a result, the gear provided on the feed screw and the intermediate gears cease to be rotated. For this reason, the rotational gear of the drive motor gradually undergoes application of the load. This load is gradually increased to become an overload, by means of the intermediate gears and by way of a spring. This brings about a state wherein a detecting plate connected to the spring is caused to project outside the box concerned. Changes in area of this projected portion of the detecting plate are detected or sensed by a microswith installed outside the drive motor. When the area of that projection has reached a specified value, a stop signal is delivered from the microswitch to the drive motor, thereby stopping the operation of the syringe pump apparatus.
In the conventional syringe pump apparatus having the described construction, the structure or construction of the halting mechanism becomes very complicated and, at the same time, transmitting stages until the pumping operation is stopped are very large in number. Accordingly, there arises a problem that a large amount of time (6 to 8 hours) is required to be spent from the stoppage of the slide to the halt of the pumping operation.